Semiconductor device using high-dielectric-constant material and method of manufacturing the same

ABSTRACT

A semiconductor device includes a MOS transistor, interlayer dielectric film, first and second high-dielectric-constant films, and first and second conductive films. The MOS transistor is formed on a semiconductor substrate. The interlayer dielectric film is formed on the semiconductor substrate so as to cover the MOS transistor. The first high-dielectric-constant film is formed on the interlayer dielectric film and has an opening portion that reaches the interlayer dielectric film. The first conductive film contains a metal element and is formed to be partially embedded in the opening portion. The second high-dielectric-constant film is formed on the first conductive film. The second conductive film is formed on the second high-dielectric-constant film.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based upon and claims the benefit of priorityfrom the prior Japanese Patent Application No. 2001-383469, filed Dec.17, 2001, the entire contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a semiconductor device andmethod of manufacturing the same and, more particularly, to a techniquefor improving the reliability of a DRAM (Dynamic Random Access Memory).

[0004] 2. Description of the Related Art

[0005] The micropatterning technology for semiconductor devices isremarkably developing in recent years. Especially, development of themicropatterning technology for DRAMs has been accelerated than ever.Accordingly, to ensure a sufficient capacitance of a capacitor in alimited occupation area, use of high-dielectric-constant materials forthe capacitor insulating films of cell capacitors has been examined. Inaddition, metal electrodes which can enhance the characteristics ofhigh-dielectric-constant materials at maximum have been developed inplace of conventional silicon electrodes.

[0006] A capacitor structure having a capacitor insulating film, using ahigh-dielectric-constant material, and a metal electrode is proposed in,e.g., Y. Fukuzumi et al., “Linear-Supported Cylinder (LSC) Technology toRealize Ru/Ta₂O₅/Ru Capacitor for Future DRAMs”, IEDM 2000, p. 793. AnMIM capacitor having an Ru/Ta₂O₅/Ru structure is proposed here.

[0007] According to the proposed structure, the adhesion between aninterlayer dielectric film and a storage node electrode using rutheniumis increased by using a liner material. This structure can prevent,e.g., a wet etchant from soaking between the storage node electrode andthe interlayer dielectric film. However, since liner material depositionand removal steps are necessary, the number of processes increases.Additionally, the liner material is not sufficiently resistant tooxidation. Hence, in the Ta₂O₅ film deposition step or high-temperatureannealing step in an oxygen atmosphere, the plug material immediatelyunder the cell capacitor may sometimes oxidizes and degrades. As aconsequence, the reliability of a memory cell tends to be low.

BRIEF SUMMARY OF THE INVENTION

[0008] A semiconductor memory device according to an aspect of thepresent invention comprises:

[0009] a MOS transistor formed on a semiconductor substrate;

[0010] an interlayer dielectric film formed on the semiconductorsubstrate so as to cover the MOS transistor;

[0011] a first high-dielectric-constant film formed on the interlayerdielectric film and having an opening portion that reaches theinterlayer dielectric film;

[0012] a first conductive film containing a metal element and formed tobe partially embedded in the opening portion;

[0013] a second high-dielectric-constant film formed on the firstconductive film; and

[0014] a second conductive film formed on the secondhigh-dielectric-constant film.

[0015] A method for fabricating a semiconductor device according to anaspect of the present invention comprises:

[0016] forming a first interlayer dielectric film on a semiconductorsubstrate;

[0017] forming a contact plug in the first interlayer dielectric film;

[0018] forming a first high-dielectric-constant film on the firstinterlayer dielectric film;

[0019] forming a second interlayer dielectric film on the firsthigh-dielectric-constant film;

[0020] forming, in the second interlayer dielectric film, a trenchportion so deep as to reach the first interlayer dielectric film toexpose an upper surface of the contact plug to a bottom surface of thetrench portion;

[0021] forming a storage node electrode on the bottom surface and a sidesurface of the trench portion using a material containing a metalelement belonging to a platinum group, the firsthigh-dielectric-constant film being substantially formed from a materialhaving a higher adhesion to the storage node electrode than to the firstand second interlayer dielectric films;

[0022] removing the second interlayer dielectric film by etching usingthe first high-dielectric-constant film as an etching stopper;

[0023] forming a capacitor insulating film on the storage node electrodeusing a high-dielectric-constant material; and

[0024] forming a plate electrode on the capacitor insulating film usinga material containing a metal element.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0025]FIG. 1A is a plan view of a DRAM according to the first embodimentof the present invention;

[0026]FIG. 1B is a sectional view taken along a line 1B-1B in FIG. 1A;

[0027]FIGS. 2A to 2G are sectional views sequentially showing the stepsin manufacturing the DRAM according to the first embodiment of thepresent invention;

[0028]FIG. 2H is a sectional perspective view of FIG. 2G;

[0029]FIG. 2I is a sectional view showing the step in manufacturing theDRAM according to the first embodiment of the present invention;

[0030]FIG. 2J is a sectional perspective view of FIG. 2I;

[0031]FIGS. 2K to 2O are sectional views sequentially showing the stepin manufacturing the DRAM according to the first embodiment of thepresent invention;

[0032]FIG. 2P is a sectional perspective view of FIG. 2O;

[0033]FIGS. 2Q to 2U are sectional views sequentially showing the stepin manufacturing the DRAM according to the first embodiment of thepresent invention;

[0034]FIGS. 3A and 3B are enlarged partial sectional views respectivelyshowing a conventional DRAM structure and the structure of the DRAMaccording to the first embodiment; and

[0035]FIG. 4 is a sectional view of a DRAM according to the secondembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0036] A semiconductor device according to the first embodiment of thepresent invention will be described with reference to FIGS. 1A and 1B.FIG. 1A is a plan view of a DRAM which employs a double-surface-cylinderstacked capacitor structure for a cell capacitor. FIG. 1B is a sectionalview taken along a line 1B-1B in FIG. 1A.

[0037] As shown in FIGS. 1A and 1B, a plurality of element regions AAwhere memory cells should be formed stagger in a silicon substrate 10.Referring to FIG. 1A, hatched regions indicate the element regions AA.Regions except the element regions AA are element isolation regions STI.

[0038] Gate electrodes 11 are formed on the silicon substrate 10 withgate insulating films 12 interposed therebetween. Each gate electrode 11has a two-layered structure including, e.g., a polysilicon film 11 a andtungsten film (W) 11 b. The gate electrodes 11 are formed into a stripethat extends across the plurality of element regions AA in a directionperpendicular to the longitudinal direction of the element regions AA.Each gate electrode 11 functions as a word line WL and is connected to arow decoder (not shown). Impurity diffusion layers (not shown) servingas source and drain regions are selectively formed in the siliconsubstrate 10; thereby forming cell transistors.

[0039] A silicon nitride film 13 covers the upper and side surfaces ofthe gate electrode 11 of each cell transistor. In addition, aninterlayer dielectric film 14 flush with the upper surface of thesilicon nitride film 13 is formed on the silicon substrate 10. Cellcontact plugs 15 and 16 connected to the source and drain regions ofeach cell transistor are formed in the interlayer dielectric film 14.

[0040] A metal diffusion barrier film 17 is formed on the interlayerdielectric film 14 and silicon nitride film 13. An interlayer dielectricfilm 18 is formed on the metal diffusion barrier film 17. The metaldiffusion barrier film 17 is formed from, e.g., a silicon nitride film.A bit line contact plug 19 that reaches the contact plug 16 is formed inthe interlayer dielectric film 18. The bit line contact plug 19 connectsthe contact plug 16 to a bit line BL. The bit line contact plug 19 ismade of, e.g., a barrier metal film 19 a having a TiN/Ti multilayeredstructure and a tungsten film 19 b. A sidewall insulating film 20 isformed between the bit line contact plug 19 and the interlayerdielectric film 18 and between the bit line contact plug 19 and metaldiffusion-barrier film 17. The sidewall insulating film 20 is made of,e.g., a silicon nitride film.

[0041] Metal interconnection layers 21 serving as the bit lines BL areformed on the interlayer dielectric films. 18. A silicon nitride film 22is formed on each metal interconnection layer 21. The bit lines BL areformed into a strip in a direction perpendicular to the word lines WL.Each bit line BL is electrically connected to the plurality of bit linecontact plugs 19 and also to a column selector (not shown). Note thatsilicon oxide films (not shown) flush with the upper surfaces of thesilicon nitride films 22 are formed on the interlayer dielectric films18 between the bit lines BL adjacent to each other.

[0042] Node contact plugs 23 which extend to contact plugs 15 throughthe silicon oxide films, interlayer dielectric films 18, and metaldiffusion barrier films 17 are formed. Each node contact plug 23connects the contact plug 15 to the storage node electrode of a cellcapacitor and has a multilayered structure of, e.g., TiN films 23 a and23 b. Note that the node contact plug 23 has a cavity region filled witha silicon nitride film 24 and tantalum oxide film (Ta₂O₅ film) 25. Asidewall insulating film 26 made of, e.g., a silicon nitride film isformed on the sidewall of the node contact plug 23.

[0043] A storage node electrode 27 of a double-surface-cylinder cellcapacitor is formed on each node contact plug 23. The storage nodeelectrode 27 is formed using, e.g., a platinum group element such asruthenium (Ru) to fill the cavity region of the node contact plug 23. Aplatinum group element is used as the capacitor electrode material toexploit the maximum characteristics of a high-dielectric-constant filmor ferroelectric film such as a Ta₂O₅ film serving as a capacitorinsulating film.

[0044] The silicon nitride films 24 and Ta₂O₅ films 25 serving asetching stopper films are formed on the silicon nitride films 22 onwhich no storage node electrodes 27 are present and on the silicon oxidefilms between the bit lines BL. A capacitor insulating film 30 is formedon the storage node electrodes 27. A plate electrode 31 is formed on thecapacitor insulating film 30. Thus, double-surface-cylinder stackedcapacitors are formed. Note that the capacitor insulating film 30 isformed from, e.g., a Ta₂O₅ film, and the plate electrode 31 is formedfrom a ruthenium film.

[0045] The distance between the adjacent word lines WL, the width ofeach bit line BL, the width of each element isolation region STI, andthe like are generally designed on the basis of the fabrication processsize in terms of process. Let F be the minimum fabrication size. Sincetwo cell transistors which share a drain region are formed in oneelement region AA, the longitudinal width of the element region AA is 5F. Cell capacitors whose longitudinal size is about 3 F are densely laidout in an array such that they are adjacent at a layout interval of 4 Fin the direction of bit lines BL.

[0046] A plate adhesion layer 32 such as a Ta₂O₅film is formed on theplate electrode 31. An interlayer dielectric film is formed on the plateadhesion layer 32. Metal interconnection layers 34 are formed on theinterlayer dielectric film 33. Each -metal interconnection layer has amultilayered structure including, e.g., a TiN film 34 a and tungstenfilm 34 b. An interlayer dielectric film 35 is further formed on theinterlayer dielectric film 33. Thus, a DRAM is formed.

[0047] A method of manufacturing the DRAM with the above structure willbe described next with reference to FIGS. 2A to 2U. FIGS. 2A to 2U,except FIGS. 2H, 2J, and 2P, are sectional views sequentially showingthe step in manufacturing the DRAM. FIGS. 2H, 2J, and 2P are sectionalperspective views corresponding to FIGS. 2G, 2I, and 2O, respectively.

[0048] First, as shown in FIG. 2A, the element isolation region STI isformed in a memory cell array region in the silicon substrate 10. A MOStransistor is formed by a known technique. More specifically, a siliconoxide film serving as the gate insulating film 12 is formed by, e.g.,thermal oxidation. Next, the polysilicon film 11 a and tungsten film 11b are deposited on the gate insulating film 12. The polysilicon film 11a and tungsten film 11 b are patterned to form the plurality of gateelectrodes 11 having a stripe shape. After that, an impurity isselectively doped into the silicon substrate 10 by ion implantation toform impurity diffusion layers (not shown) serving as source and drainregions. The MOS transistor thus formed functions as the cell transistorof a DRAM memory cell. Next, the silicon nitride film 13 is formed onthe upper and side surfaces of each gate electrode 11 by, e.g., CVD(Chemical Vapor Deposition).

[0049] As shown in FIG. 2B, the silicon oxide film 14 serving as aninterlayer dielectric film is formed on the silicon substrate 10 so asto cover the silicon nitride films 13. Then, the silicon oxide film 14on each silicon nitride film 13 is removed by CMP (Chemical MechanicalPolishing) using the silicon nitride film 13 as a stopper. Subsequently,the silicon oxide films 14 in cell contact plug formation regions areremoved in self-align manner with respect to the gate electrode 11 usinglithography and etching.

[0050] As shown in FIG. 2C, amorphous silicon doped with arsenic (As) isdeposited on the silicon substrate 10, silicon nitride films 13, andinterlayer dielectric films 14. The cell contact plugs 15 and 16 areformed by removing the amorphous silicon on the silicon nitride films 13by, e.g., CMP.

[0051] As shown in FIG. 2D, the silicon nitride thin film 17 serving asa metal diffusion barrier film is formed on the silicon nitride films 13and cell contact plugs 15 and 16. For example, the silicon oxide film 18serving as an interlayer dielectric film is-formed on the siliconnitride thin film 17. The silicon oxide film 18 immediately above thecell contact plug 16 (bit line contact plug formation region) is removedto form an opening portion 36 by lithography and etching.

[0052] As shown in FIG. 2E, the silicon nitride thin film 20 serving asa sidewall insulating film is formed on the interlayer dielectric film18 and in the opening portion 36. The silicon nitride film 20 on thesilicon oxide film 18 and the silicon nitride films 20 and 17 on thebottom surface of the opening portion 36 are removed by etch back usingRIE (Reactive Ion Etching). As a result, the cell contact plug 16 isexposed to the bottom portion of the opening portion 36.

[0053] Next, as shown in FIG. 2F, the TiN/Ti multilayered film 19 aserving as a barrier metal film is formed on the silicon oxide film 18and in the opening portion 36. Subsequently, the tungsten film 19 b isformed to fill the opening portion 36. The TiN/Ti multilayered film 19 aand tungsten film 19 b on the silicon oxide film 18 are removed by CMPor the like such that they remain only in the opening portion 36,thereby forming the bit line contact plug 19.

[0054] As shown in FIG. 2G, the tungsten film 21 and silicon nitridefilm 22 serving as the bit lines BL are formed on the silicon oxide film18 and bit line contact plug 19. The tungsten film 21 and siliconnitride film 22 are patterned into a stripe shape running in a directionperpendicular to the word lines WL (gate electrodes 11) usinglithography and RIE, thereby completing the bit lines BL. A siliconoxide film is deposited on the bit lines BL and on the silicon oxidefilms 18 between the bit lines BL by HDP (High Density Plasma)-CVD orthe like. The silicon oxide film on the silicon nitride film 22 isremoved by CMP using the silicon nitride film 22 on the tungsten film 21as a stopper. Consequently, the structure shown in FIG. 2G is completed.FIG. 2H is a sectional perspective view of a region A1 in FIG. 1A, whichcorresponds to the step shown in FIG. 2G. As shown in FIG. 2H, the metalinterconnection layers 21 (bit lines BL) and silicon nitride films 22having a stripe pattern perpendicular to the word lines WL are presentimmediately above the cell contact plugs 16 connected to the drainregions of cell transistors. On the other hand, silicon oxide films 37having a stripe pattern perpendicular to the word lines WL are presentimmediately above the contact plugs 15 connected to the source regionsof cell transistors. The silicon oxide films 37 fill the regions betweenthe adjacent bit lines BL.

[0055] Next, as shown in FIG. 2I, the silicon oxide films 18 and 37immediately above the cell contact plugs 15 (node contact plug formationregions) are removed by lithography and etching to form opening portions38. In this step, selective etching is used such that the siliconnitride film is etched at a low etching rate, and the silicon oxide filmis etched at a high etching rate, thereby forming the opening portions38 self-aligning to the bit lines BL. FIG. 2J is a sectional perspectiveview of the region A1 in FIG. 1A, which corresponds to the step shown inFIG. 2I. As shown in FIG. 2J, the plurality of opening portions 38 arepresent in the silicon oxide films 18 and 37 between the bit lines BL.The silicon nitride film 17 is exposed to the bottom surfaces of theopening portions 38. In addition, the metal inter-connection layers 21serving as the bit lines BL are exposed to the side surfaces of theopening portions 38 on the bit line BL sides. Hence, when node contactplugs are directly formed in the opening portions 38, the node contactplugs and bit lines BL short-circuit. To prevent this, the siliconnitride thin films 26 serving as sidewall insulating films are formed onthe silicon oxide films 37 and silicon nitride films 22 and in theopening portions 38, as shown in FIG. 2K. The silicon nitride film 26 onthe silicon oxide films 37, silicon nitride films 22, and siliconnitride films 26 and 17 on the bottom surfaces of the opening portions38 are removed by etch back using RIE. As a result, the cell contactplugs 15 are exposed to the bottom portions of the opening portions 38.The silicon nitride films 26 remain only on the side surfaces of theopening portions 38.

[0056] As shown in FIG. 2L, a Ti film is formed on the silicon oxidefilms 37 and silicon nitride films 22 and in the opening portions 38 by,e.g., sputtering. Annealing is performed, and simultaneously, thesurface is nitrided to form the TiN/Ti multilayered film 23 a.Subsequently, the TiN film 23 b is formed on the TiN/Ti multilayeredfilm 23 a by CVD or the like. At this time, for example, a gap about ¼the opening size of the opening portion 38 is preferably left withoutcompletely filling the opening portion 38 with the TiN film 23 b.

[0057] After that, a sacrificial film such as a resist is coated on theTiN film 23 and in the opening portions 38. The sacrificial film, TiN/Timultilayered film 23 a, and TiN film 23 b on the silicon oxide films 37and silicon nitride films 22 are removed. After that, by removing thesacrificial films in the opening portions 38 by, e.g., wet etching, thenode contact plugs 23 each having a gap inside are completed, as shownin FIG. 2M.

[0058] As shown in FIG. 2N, for example, the silicon nitride film 24serving as a RIE stopper film is formed on the silicon oxide films 37and silicon nitride films 22 and in the opening portions 38 by plasmaCVD or the like. The gaps in the node contact plugs 23 need not alwaysbe filled with the silicon nitride film 24. Subsequently, for example,the Ta₂O₅ film 25 serving as a wet stopper film is formed on the siliconnitride film 24.

[0059] Next, as shown in FIG. 2O, an interlayer sacrificial film 39 isdeposited on the Ta₂O₅ film 25. The interlayer sacrificial film is,e.g., a silicon oxide film doped with boron or phosphorus. Theinterlayer sacrificial film 39 and Ta₂O₅ film 25 in cell capacitorformation regions are removed using lithography and selective RIE. Thesilicon oxide film and tantalum oxide film can be etched under the sameRIE conditions. Hence, etching temporarily stops at the silicon nitridefilm 24 serving as an RIE stopper film. FIG. 2P is a sectionalperspective view of the region A1 in FIG. 1A, which corresponds to thestep shown in FIG. 2O. As shown in FIG. 2P, a plurality of openingportions 40 are formed in the interlayer sacrificial film 39. Thesilicon nitride film 24 is exposed to the bottom portion of each openingportion 40.

[0060] As shown in FIG. 2Q, the silicon nitride film 24 exposed to thebottom portion of each opening portion 40 is removed by RIE or the like.As a result, the node contact plugs 23 are exposed to the bottomportions of the opening portions 40.

[0061] As shown in FIG. 2R, the ruthenium film 27 serving as a storagenode electrode is formed on the interlayer sacrificial film 39 and inthe opening portions 40. In addition, a sacrificial film 41 such as aresist is formed on the storage node electrode 27 and interlayersacrificial film 39. After that, the ruthenium film 27 and sacrificialfilm 41 on the interlayer sacrificial film 39 are removed by CMP or thelike such that they remain only in the opening portions 40.

[0062] As shown in FIG. 2S, the interlayer sacrificial film 39 isremoved by wet etching using, e.g., a buffer solution prepared by mixingdiluted HF and NH₄F. Unlike RIE, the silicon oxide film and tantalumoxide film have a high etching selectivity for wet etching. Hence, thewet etching in this step stops at the Ta₂O₅ film 25 serving as a wetstopper film. As a consequence, the double-surface-cylinder storage nodeelectrodes 27 are completed.

[0063] As shown in FIG. 2T, the sacrificial film 41 remaining in thecylinder of each storage node electrode 27 is removed by resist ashingand wet process. The high-dielectric-constant film 30 such as a Ta₂O₅film serving as a capacitor insulating film and the metal film 31 suchas a ruthenium film serving as a plate electrode are formed on thestorage node electrodes 27. Subsequently, for example, the Ta₂O₅ film 32serving as a plate adhesion layer is formed on the plate electrode 31.As a result, double-surface-cylinder cell capacitors as shown in FIG. 2Tare completed.

[0064] The plate electrode 31 is patterned by lithography and etching.The unwanted plate adhesion layer 32, capacitor insulating film 30, wetstopper film 25, and RIE stopper film 24 are also simultaneously removedtogether with the plate electrode 31. As shown in FIG. 2U, theinterlayer dielectric film 33 that covers the cell capacitors is formedfrom, e.g., a silicon oxide film-and planarized by CMP or the like.After that, multilayered interconnections and interlayer dielectric filmare formed to complete the DRAM shown in FIGS. 1A and 1B.

[0065] According to the semiconductor device having the abovearrangement formed by the above manufacturing method, the followingeffects are obtained.

[0066] (1) The conventional liner material can be omitted. In the DRAMaccording to this embodiment, a metal compound (Ta₂O₅ in thisembodiment) is used as the wet stopper film 25 that is conventionallyoften a silicon nitride film or the like. For this reason, sufficientadhesion can be ensured between the wet stopper film 25 and the storagenode electrode 27 formed using a metal material (ruthenium in thisembodiment) such as a platinum group element. More specifically, achemical solution can be prevented from soaking into the interfacebetween the storage node electrode 27 and the wet stopper film 25 andcorrode the underlayer in wet-etching the interlayer sacrificial film 39described with reference to FIG. 2S. Hence, the conventional linermaterial can be omitted, the manufacturing process can be simplified,and the manufacturing yield can be increased.

[0067] (2) The reliability of the cell capacitor can be increased. Thiswill be described with reference to FIGS. 3A and 3B. FIGS. 3A and 3B aresectional views of a region where particularly the wet stopper film andstorage node electrode in the DRAM come into contact in forming acapacitor insulating film. FIG. 3A shows the conventional structure, andFIG. 3B shows the structure according to this embodiment. In forming thecapacitor insulating film 30, the storage node electrode 27 and wetstopper film 25 are exposed to the surface. When ahigh-dielectric-constant film such as a Ta₂O₅ film serving as thecapacitor insulating film is to be deposited by CVD, an initial layerserving as the “nucleus” of growth must be formed at the early stage ofgrowth (this is called an “incubation time”). The incubation timedepends on the underlying material. For example, the incubation time iszero on a ruthenium film but requires several ten sec on a silicon oxidefilm or silicon nitride film. In the conventional structure, a siliconnitride film is generally used as the wet stopper film 25. Hence, thehigh-dielectric-constant film 30 such as a Ta₂O₅ film serving as acapacitor insulating film is formed on the metal film 27 such as aruthenium film serving as a storage node electrode and on the siliconnitride film 25 serving as a wet stopper film. At this time, theincubation time is generated only on the wet stopper film 25. As aresult, a film thickness d1 of the Ta₂O₅ film 30 on the wet stopper film25 is smaller than a film thickness d2 on the storage node electrode 27in correspondence with the incubation time, as shown in FIG. 3A. Then,the Ta₂O₅ film 30 formed thin at a corner portion (region A2 in FIG. 3A)where the storage node electrode 27 and wet stopper film 25 come intocontact is readily affected by stress, resulting in a decrease inreliability of the cell capacitor. However, in the structure accordingto this embodiment, the wet stopper film 25 is formed from the samematerial as that of the capacitor insulating film 30(high-dielectric-constant film such as a Ta₂O₅ film). Hence, noincubation time is generated either on the wet stopper film 25 or on thestorage node electrode 27. As a result, the film thickness d1 of theTa₂O₅ film 30 on the wet stopper film 25 is the same as the filmthickness d2 on the storage node electrode 27, as shown in FIG. 3B. At acorner portion (region A3 in FIG. 3B) where the storage node electrode27 and wet stopper film 25 come into contact, the capacitor insulatingfilm 30 can be regarded to be thicker in correspondence with the wetstopper film 25. Hence, the capacitor insulating film particularly atthe corner portion is thick, and the strength against stress in thisregion can be increased. This increases the reliability of the cellcapacitor.

[0068] (3) Corrosion of the underlying film when the function of the wetstopper film is insufficient can be minimized. In this embodiment, theinterlayer sacrificial film 39 used in forming the storage nodeelectrode is a silicon oxide film doped with boron and/or phosphorus. Onthe other hand, the interlayer dielectric film 37 between the adjacentbit lines BL is a silicon oxide film formed by HDP-CVD without dopingthe impurity. The etching rate for the silicon oxide film by a dilutedHF-NH₄F buffer solution can be increased to about 100 times by dopingboron or phosphorus. Hence, the wet etching time of the interlayersacrificial film 39 described with reference to FIG. 2S can be largelyshortened. In this case, even when the wet stopper film 25 has a defectsuch as a pinhole, and the etchant corrodes the underlying layer beyondthe wet stopper film 25, the corrosion amount of the underlying siliconoxide film 37 can be minimized because the silicon oxide film isundoped. As a result, the manufacturing yield of DRAMs can be increased.

[0069] (4) Stress generated in the node contact plug portion can berelaxed. TiN that forms the node contact plug generates a large stressdue to the peripheral influence because of the characteristics of TiN.For this reason, when the node contact plug is formed by completelyfilling the contact hole with the TiN film, cracks may be generated inthe interlayer dielectric film in the subsequent annealing step or thelike. In this embodiment, however, the node contact plug 23 has a gapinside. That is, as described with reference to FIG. 2L, the TiN film 23b does not completely fill the opening portion 38. Hence, the TiN film23 b itself can have a small thickness and suppress stress. In addition,stress on the TiN film 23 b can be relaxed by the gap in the plug.Hence, the influence on the other regions including the interlayerdielectric film can be minimized. Consequently, the manufacturing yieldof DRAMs can be increased.

[0070] (5) Any damage to the underlying layer by RIE in forming anopening portion for a storage node electrode can be prevented. In theDRAM according to this embodiment, the RIE stopper film 24 is formedfrom a silicon nitride film. As the size of a semiconductor devicebecomes smaller, the storage node electrode of a stacked cell capacitortends to be higher (deeper). For example, in a DRAM according to thedesign rule of 0.13 μm, the height of a storage node electrode can beabout 1 μm. That is, in the step described with reference to FIG. 2O,the opening portions 40 having a depth of about 1 μm are formed in theinterlayer sacrificial film 39. If no etching stopper is used, theopening portion 40 that reaches the node contact plug 23 must be formedby time control. However, since the opening portion 40 is deep, thebottom portion of the opening is inevitably damaged by time control RIE.More specifically, the upper surface of the node contact plug 23 may beundesirably exposed to RIE, or the silicon oxide film 37 isunnecessarily etched. In this embodiment, however, the thin RIE stopperfilm 24 is formed. RIE is executed while using the RIE stopper film 24as an etching stopper, thereby forming the opening portions 40 in theinterlayer sacrificial film 39. After that, the RIE stopper film 24 isremoved by time control RIE until the node contact plug 23 is exposed.When the opening portions 40 are formed by two-step RIE, and the thinRIE stopper film is etched by the final RIE process, the degree ofdamage to the bottom portion of each opening portion 40 can beminimized. As a result, the manufacturing yield of DRAMs can beincreased. Note that the RIE stopper film 24 may be formed on the wetstopper film 25.

[0071] (6) Any harmful influence by metal atoms can be prevented. Alongwith the recent size reduction and diversification of semiconductordevices, there are many opportunities of use of new metal elementsincluding ruthenium, which are not popular before, for DRAMs. However,such metal elements, e.g., ruthenium have a relatively high diffusionspeed in a silicon oxide film. Hence, ruthenium atoms in the storagenode electrode 27 may diffuse in the interlayer dielectric film andreach the semiconductor substrate. These metal atoms may cause badinfluence, e.g., leakage in cell transistors. In the DRAM according tothis embodiment, however, the metal diffusion barrier film 17 andsidewall insulating films 20 and 26, which are formed from siliconnitride films, are arranged. In the silicon nitride film, the diffusionspeed of ruthenium is relatively low, as is known. Hence, these siliconnitride films can prevent ruthenium from is reaching the semiconductorsubstrate surface. As a result, the manufacturing yield of DRAMs can beincreased, and stable DRAM operation can be realized.

[0072] (7) The adhesion between the plate electrode 31 and theinterlayer dielectric film can be increased. As described above, toexploit the characteristics of a high-dielectric-constant material orferroelectric material serving as a capacitor insulating film atmaximum, a metal element of a platinum group or the like, includingruthenium, must be used as the plate electrode material. However, thesematerials have a low adhesion to, e.g., a silicon oxide film serving asan interlayer dielectric film. Hence, the plate electrode may peel offfrom the interlayer dielectric film in annealing or the like, resultingin a fatal defect for a semiconductor device. However, according to thisembodiment, the plate adhesion layer 32 made of a metal oxide, e.g., aTa₂O₅ film, is formed between the plate electrode 31 and the interlayerdielectric film 33. Hence, the adhesion between the plate electrode 31and the interlayer dielectric film 33 increases, and the manufacturingyield of DRAMs can be increased.

[0073] (8) The reliability of the capacitor insulating film can beincreased. In manufacturing a semiconductor device, annealing in ahydrogen atmosphere is often executed after formation of finalmultilayered interconnections in order to improve the characteristics oftransistors. In this case, hydrogen atoms may enter the capacitorinsulating film and degrade it. According to this embodiment, however,the plate adhesion layer 32 as a metal oxide film is formed, asdescribed above in effect (7). This can prevent hydrogen atoms fromdegrading the capacitor insulating film.

[0074] Note that the plate adhesion layer 32 need not always be formedfrom the same material as that of the capacitor insulating film, as inthis embodiment. However, if the capacitor insulating film, wet stopperfilm, and plate adhesion layer are made of the same material as much aspossible, the number of film forming apparatuses in the semiconductormanufacturing line can be reduced. As a result, the manufacturing costof semiconductor devices can be reduced.

[0075] A semiconductor device according to the second embodiment of thepresent invention will be described next with reference to FIG. 4 whileexemplifying a DRAM. FIG. 4 is a sectional view of a DRAM according tothis embodiment.

[0076] As shown in FIG. 4, in the DRAM according to this embodiment, anode contact plug 23 of the first embodiment is formed from a TiN/Tifilm 23 a and ruthenium film 23 c. The remaining parts of the structureare the same as in the first embodiment, and a detailed descriptionthereof will be omitted. The DRAM according to this embodiment can beformed by depositing the ruthenium film 23 c in place of a TiN film 23 bin the step shown in FIG. 2L.

[0077] According to this embodiment, the following effects can beobtained in addition to effects (1) to (8) described in the firstembodiment.

[0078] (9) The adhesion between the node contact plug and the storagenode electrode can be increased. In this embodiment, the node contactplug is formed using ruthenium, i.e., the same material as that of thestorage node electrode. That is, no material difference is presentbetween the node contact plug and the storage node electrode. For thisreason, for example, formation of, e.g., an oxide film at the interfacebetween the storage node electrode and the node contact plug can beprevented. Hence, the adhesion and electrical conductivity between thestorage node electrode and the node contact plug can greatly beincreased. As a result, the manufacturing yield of DRAMs can beincreased, and the performance can be improved.

[0079] (10) Stress generated in the node contact plug portion can berelaxed. This effect is the same as effect (4) described in the firstembodiment. When the node contact plug is formed from ruthenium, thefollowing advantages can particularly be obtained. When a conductivefilm including a platinum group element such as ruthenium is depositedby CVD, the growth temperature is relatively low and about 300° C. Afterformation of the node contact plug, annealing at a higher temperature isnormally executed in the step of forming a high-dielectric-constant filmsuch as a Ta₂O₅ film or in the step of forming multilayeredinterconnections. The volume of a ruthenium film immediately afterformation readily shrinks due to heat. Hence, when the node contact plugis formed from a ruthenium film that completely fills the plug portion,stress more than that in use of a TiN film is generated. This posesserious problems. For example, cracks are formed in the interlayerdielectric film, or peeling occurs at the interface between the metalfilm and the insulating film on contact side surface. However, when thenode contact plug has a gap, as in this embodiment, the ruthenium filmitself can be made thin. This suppresses generation of stress and alsorelaxes generated stress. Consequently, the influence on the otherregions such as the interlayer dielectric film can be minimized. Hence,the manufacturing yield of DRAMs can be increased.

[0080] As described above, according to this embodiment, themanufacturing process of the semiconductor device can be simplified, andthe reliability of the semiconductor device can be increased. In thefirst and second embodiments, ruthenium (Ru) is used as the capacitorelectrode material, and a tantalum oxide film (Ta₂O₅ film) formed from ahigh-dielectric-constant material is used as the material of thecapacitor insulating film. A “high-dielectric-constant material” means amaterial with a higher dielectric constant than that of silicon nitride.For the capacitor electrode material, any other platinum group such asplatinum (Pt), iridium (Ir), palladium (Pd), osmium (Os), or rhodium(Rh), any other conductive film represented by rhenium (Re), or an alloythereof or a conductive metal oxide thereof, such as Sr—Ru—O (SRO),RuO₂, or IrO₂ can be used. For the capacitor insulating film, ahigh-dielectric-constant film or ferroelectric film of an oxidecontaining any one of barium (Ba), strontium (Sr), lead (Pb), titanium(Ti), zirconium (Zr), and tantalum (Ta), aluminum (Al) for example,Ta—Ti—O, barium titanate-strontium (Ba—Sr—Ti—O: BST), strontium titanate(Sr—Ti—O: STO), lead zirconate titanate (Pb—Zr—Ti—O: PZT), or strontiumtantalate-bismuth (Sr—Bi—Ta—O: SBT), alumina (Al₂O₃) can be used.

[0081] In the above embodiments, a cylinder type capacitor structure hasbeen exemplified. However, the embodiment of the present invention isnot limited to this and can also be applied to a pillar type or concavetype stacked capacitor. The embodiment of the present invention can beapplied not only to a DRAM but also to, e.g., an EEPROM (ElectricallyErasable and Programmable Read Only Memory), Ferroelectric RAM, MRAM(Magneto-resistive RAM), and DRAM embedded logic. The embodiment of thepresent invention can be applied not only to a semiconductor memory butalso widely to general semiconductor devices using the abovehigh-dielectric-constant material/ferroelectric material and platinumgroup material.

[0082] Additional advantages and modifications will readily occur tothose skilled in the art. Therefore, the invention in its broaderaspects is not limited to the specific details and representativeembodiments shown and described herein. Accordingly, variousmodifications may be made without departing from the spirit or scope ofthe general inventive concept as defined by the appended claims andtheir equivalents.

1-17. (Canceled)
 18. A semiconductor device comprising: a MOS transistorformed on a semiconductor substrate; an interlayer dielectric filmformed on the semiconductor substrate so as to cover the MOS transistor;a contact plug which includes a first conductive film and a buried film,the first conductive film being formed on a side surface and bottomsurface of a contact hole made in the interlayer dielectric film, theburied film being formed in a region surrounded by the first conductivefilm in the contact hole and formed from a material different from thatof the first conductive film; a second conductive film formed on theinterlayer dielectric film and electrically connected to the firstconductive film; a first high-dielectric-constant film formed on thesecond conductive film; a third conductive film formed on the firsthigh-dielectric-constant film.
 19. The device according to claim 18,further comprising a second high-dielectric-constant film formed on thethird conductive film.
 20. The device according to claim 18, wherein thefirst conductive film is substantially formed from a metal elementbelonging to a platinum group.
 21. The device according to claim 18,wherein the first conductive film is substantially formed from aruthenium film.
 22. The device according to claim 18, wherein the firstand second conductive films are substantially formed from the samematerial.
 23. The device according to claim 18, further comprising afirst metal diffusion preventing film which is formed on a side surfaceof the contact plug to prevent metal atoms contained at least one of thefirst and second conductive films from diffusing into the MOStransistor.
 24. The device according to claim 23, wherein the firstmetal diffusion preventing film in substantially formed from a siliconnitride film.
 25. (Canceled).
 26. The device according to claim 18,wherein a plurality of capacitor structures each containing the secondand third conductive films and the first high-dielectric-constant filmare laid out in an array at an interval smaller than a capacitor width.27. The device according to claim 18, wherein a plurality of capacitorstructures each containing the second and third conductive films and thefirst high-dielectric-constant film are laid out in an array at anadjacent interval substantially equal to or smaller than a minimumfabrication size.
 28. The device according to claim 18, furthercomprising a second metal diffusion preventing film which is formed inthe interlayer dielectric film so as to cover the MOS transistor andprevent metal atoms contained in at least one of the first and secondconductive films from diffusing into the MOS transistor.
 29. The deviceaccording to claim 28, wherein the second metal diffusion preventingfilm is substantially formed from a silicon nitride film.
 30. The deviceaccording to claim 28, wherein a diffusion speed of metal atomscontained in at least one of the first and second conductive films islower in the first and second metal diffusion preventing films than inthe interlayer dielectric film. 31-39. (Canceled).
 40. The deviceaccording to claim 18, wherein the second conductive film is formed onthe contact plug, and buries a part of the region surrounded by thefirst conductive film in the contact hole.
 41. The device according toclaim 18, wherein the second conductive film is a cylinder typecapacitor electrode, and an upper surface of the firsthigh-dielectric-constant film is lower than opening portion of thecylinder structure.
 42. A semiconductor device comprising: a MOStransistor formed on a semiconductor substrate; an interlayer dielectricfilm formed on the semiconductor substrate so as to cover the MOStransistor; a first ferroelectric film formed on the interlayerdielectric film and having an opening portion that reaches theinterlayer dielectric film; a first conductive film containing a metalelement and formed to be partially embedded in the opening portion; asecond ferroelectric film formed on the first conductive film; and asecond conductive film formed on the second ferroelectric film.
 43. Thedevice according to claim 42, wherein the first and second ferroelectricfilms are substantially formed from the same material.
 44. The deviceaccording to claim 42, wherein the first and second ferroelectric filmsare substantially formed from a metal compound.
 45. The device accordingto claim 42, wherein the metal element contained in the first conductivefilm belongs to a platinum group.
 46. The device according to claim 42,wherein the first conductive film is substantially formed from aruthenium film.
 47. The device according to claim 42, further comprisinga contact plug which is formed in the interlayer dielectric film so asto be in contact with the first conductive film located in the openingportion of the first ferroelectric film.
 48. The device according toclaim 47, wherein the first conductive film and the contact plug aresubstantially formed from the same material.
 49. The device according toclaim 47, wherein each of the first conductive film and the contact plugis substantially formed from a ruthenium film.
 50. The device accordingto claim 42, further comprising a third ferroelectric film formed on thesecond conductive film.
 51. The device according to claim 50, whereinthe first and third ferroelectric films are substantially formed fromthe same material.
 52. The device according to claim 50, wherein thefirst and third ferroelectric films are substantially formed from thesame material.
 53. The device according to claim 42, wherein a diffusionspeed of metal atoms contained in the first conductive film is lower inthe first ferroelectric film than in the interlayer dielectric film. 54.The device according to claim 42, further comprising a metal diffusionpreventing film which is formed in the interlayer dielectric film so asto cover the MOS transistor and prevent metal atoms contained in thefirst conductive film from diffusing into the MOS transistor.
 55. Thedevice according to claim 54, wherein the metal diffusion preventingfilm is substantially formed from a silicon nitride film.
 56. The deviceaccording to claim 54, wherein a diffusion speed of metal atomscontained in the first conductive film is lower in the metal diffusionpreventing film than in the interlayer dielectric film.
 57. The deviceaccording to claim 42, wherein the first conductive film is a cylindertype capacitor electrode, and an upper surface of the firstferroelectric film is lower than an opening portion of the cylinderstructure.